1. Field of the Invention
The present invention relates to a method of chromaticity adjustment of a display device, in particular, a method of chromaticity adjustment of a liquid crystal display device including a backlight unit.
2. Description of the Related Art
A liquid crystal display device has a structure including: a backlight unit for emitting a plane-shaped backlight beam; and a liquid crystal display panel having a plurality of pixels arranged in a matrix shape, for performing image display according to a video signal input from an external device with the backlight beam as a light source. In particular, a compact liquid crystal display device using a white LED, which is advantageous in achieving downsizing, lightweight, and low power consumption, as the light source of the backlight unit is becoming widespread rapidly.
The liquid crystal display device is configured to perform the image display corresponding to the video signal by controlling a transmission amount of the backlight beam for each pixel. For this reason, the liquid crystal display device is configured to perform the image display by maximizing the transmission amount of the backlight beam from the backlight unit in the case of performing white display. Therefore, a chromaticity tolerance of the liquid crystal display device greatly depends on a whiteness tolerance of the white LED used as the light source.
Meanwhile, LEDs produced for backlight of the liquid crystal display device exhibit a large chromaticity unevenness, and under present circumstances, the chromaticity tolerance of the LED does not satisfy the chromaticity tolerance of the liquid crystal display device or the chromaticity tolerance of the backlight which is demanded in the market. At present, white LEDs exhibiting a large chromaticity unevenness are classified into a plurality of ranks according to the magnitude of unevenness (magnitude of a deviation from a chromaticity designed value), and a □ characteristic of the liquid crystal display device is adjusted according to each rank to thereby suppress the chromaticity tolerance of the liquid crystal display device and the chromaticity tolerance of the backlight within a required range.
In recent years, there have been demands for further improvements in display quality, and also in the liquid crystal display device using a white LED, there are demands for further compliance with a narrow whiteness tolerance that suppresses unevenness in whiteness. As the compliance with the narrow whiteness tolerance, it is conceivable that, at the time of manufacturing, the whiteness and the γ characteristic are measured for each liquid crystal display device, and data on the γ characteristics is corrected based on the measured values. However, an extremely large amount of time is required in order to measure the γ characteristics of all the liquid crystal display devices at the time of manufacturing and correct the data on the γ characteristics based on the measured values, which could cause a significant reduction of manufacturing throughput.
As a technology for causing the chromaticity of the liquid crystal display device to fall within a predetermined chromaticity tolerance even when using an LED exhibiting a large chromaticity unevenness, there are technologies disclosed in Japanese Patent Application Laid-open No. 2010-181430 and Japanese Patent Application Laid-open No. 2007-128822.
Further, there is a technology disclosed in Japanese Patent Application Laid-open No. 2006-91235 as a technology for correcting the γ characteristic and the chromaticity of the backlight. In the technology disclosed in Japanese Patent Application Laid-open No. 2006-91235, a color sensor is disposed for each liquid crystal display panel, a comparison is performed between chromaticity information measured by the color sensor and a reference value of the chromaticity information, a correction is made to a color conversion table including γ characteristics based on a comparison result thereof, and the corrected color conversion table is used to generate an output value.